Denitrification by N2-fixing Spirillum lipoferum

Abstract

Forty-nine N2-fixing strains of Spirillum lipoferum isolated from a wide range of plant roots and soils were examined for reduction of NO3−. All strains reduced NO3− to NO2−. Thirty of the strains further reduced NO2− with production of gas. Examination of representative strains of the putative denitrifiers showed that they produced both N2O and C2H4 in the presence of 0.1 atm of C2H2. Strains which did not reduce NO2− with production of gas produced C2H4 but not N2O in the presence of C2H2. This is the first report of a N2-fixing bacterium able to bring about denitrification of NO3−.